From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
 id 3C7DE39ACCA9; Thu, 19 Nov 2020 23:20:25 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 3C7DE39ACCA9
From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/93917] VRP forgets range of value read from
 memory
Date: Thu, 19 Nov 2020 23:20:25 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: amacleod at redhat dot com
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: cc
Message-ID: <bug-93917-4-ORLPMB7Ien@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-93917-4@http.gcc.gnu.org/bugzilla/>
References: <bug-93917-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Thu, 19 Nov 2020 23:20:25 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D93917

Andrew Macleod <amacleod at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com

--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
This seems to be a good place to bring up a question I have.

What exactly do we want to with __builtin_unreachable across passes?

Ranger was initially starting with the previously set globally known value,=
 and
I had to disable it for pr61034.C

Basically, the routine was pre-optimized and inlined, and inlining sets the
global range based on the output from the optimizations, and when ranger
removed the code with the unreachable in it, the testcase failed.

so=20
void f(int n){
  if(n<0)__builtin_unreachable();
}
n has a global range of [0, +INF]

Is that the basic point of this?  Can we set the global range to that and
eliminate the if?

same thing for=20
  if(*n<0)__builtin_unreachable();

I see:
    _1 =3D *n_3(D);
    if (_1 < 0)
      goto <bb 3>; [INV]
    else
      goto <bb 4>; [INV]

2->3  (T) _1 :  int [-INF, -1]
2->4  (F) _1 :  int [0, +INF]

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BB 3 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
    <bb 3> :
    __builtin_unreachable ();

And we can know that _1 is [0, +INF] from then on.=20

Can we kill all these unreachables() the first time we see them if we set t=
he
range appropriately?

If not, at what point do we want to kill them?=